The present invention relates to an automatic hemming apparatus for tubular workpieces such as T-shirts, underwears, jogging shorts, free-size skirts and pants. When a tubular workpiece is supplied to the apparatus, a bottom edge of the workpiece is folded over to the inside, and the folded edge is automatically sewn or "hemmed" between a feed dog provided in a sewing bed and a presser foot facing thereto.
In a hemming apparatus for tubular workpieces of this type, it is technically most important that a folded edge of the workpiece is guided to a position spaced from a sewing needle by a predetermined distance, and adequately controlled in position so that a seam is formed in parallel with the edge, and those disclosed, for example, in Japanese Laid-Open Patent Nos. 2-95396, 4-256780, 4-256781, 2-23987 and Published Patent No. 1-1155 and U.S. Pat. No. 4,825,787 are known as such apparatuses. In the cited references, various position control technologies are disclosed for detecting an offset of the edge by a photoelectric sensor, and forcing the edge to an appropriate position according to the amount of the offset detected.
Such conventional hemming apparatuses for tubular workpieces, however, are semi-automatic, and such assisting operations of manually leading and keeping the workpiece by an operator are indispensable in order to ensure that the edge of workpiece is guided to a predetermined position. Because such assisting operation is manually performed for guiding the edge of a workpiece, the operating (sewing) efficiency is insufficient, and it also requires a certain level of experiences and skills.